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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Chapter 27. Input and Output</title><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="extensions.html" title="Part III.  Extensions" /><link rel="prev" href="ext_iterators.html" title="Chapter 26. Iterators" /><link rel="next" href="ext_demangling.html" title="Chapter 28. Demangling" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter 27. Input and Output</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ext_iterators.html">Prev</a> </td><th width="60%" align="center">Part III. 
  Extensions
  
</th><td width="20%" align="right"> <a accesskey="n" href="ext_demangling.html">Next</a></td></tr></table><hr /></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.io"></a>Chapter 27. Input and Output</h2></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="section"><a href="ext_io.html#manual.ext.io.filebuf_derived">Derived filebufs</a></span></dt></dl></div><p>
    Extensions allowing <code class="code">filebuf</code>s to be constructed from
    "C" types like  FILE*s and file descriptors.
  </p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="manual.ext.io.filebuf_derived"></a>Derived filebufs</h2></div></div></div><p>The v2 library included non-standard extensions to construct
      <code class="code">std::filebuf</code>s from C stdio types such as
      <code class="code">FILE*</code>s and POSIX file descriptors.
      Today the recommended way to use stdio types with libstdc++
      IOStreams is via the <code class="code">stdio_filebuf</code> class (see below),
      but earlier releases provided slightly different mechanisms.
   </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>3.0.x <code class="code">filebuf</code>s have another ctor with this signature:
	<code class="code">basic_filebuf(__c_file_type*, ios_base::openmode, int_type);
	</code>
	 This comes in very handy in a number of places, such as
	 attaching Unix sockets, pipes, and anything else which uses file
	 descriptors, into the IOStream buffering classes.  The three
	 arguments are as follows:
	 </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "><li class="listitem"><p><code class="code">__c_file_type*      F   </code>
	      // the __c_file_type typedef usually boils down to stdio's FILE
	  </p></li><li class="listitem"><p><code class="code">ios_base::openmode  M   </code>
	      // same as all the other uses of openmode
	  </p></li><li class="listitem"><p><code class="code">int_type            B   </code>
	      // buffer size, defaults to BUFSIZ if not specified
	  </p></li></ul></div><p>
	 For those wanting to use file descriptors instead of FILE*'s, I
	 invite you to contemplate the mysteries of C's <code class="code">fdopen()</code>.
     </p></li><li class="listitem"><p>In library snapshot 3.0.95 and later, <code class="code">filebuf</code>s bring
	 back an old extension:  the <code class="code">fd()</code> member function.  The
	 integer returned from this function can be used for whatever file
	 descriptors can be used for on your platform.  Naturally, the
	 library cannot track what you do on your own with a file descriptor,
	 so if you perform any I/O directly, don't expect the library to be
	 aware of it.
     </p></li><li class="listitem"><p>Beginning with 3.1, the extra
	 <code class="classname">basic_filebuf</code> constructor and
	 the <code class="code">fd()</code> function were removed from the standard
	 filebuf.  Instead,
	 <code class="filename">&lt;ext/stdio_filebuf.h&gt;</code>
	 contains a derived class template called
	 <code class="classname">__gnu_cxx::stdio_filebuf</code>.
	 This class can be constructed from a C <code class="code">FILE*</code> or a file
	 descriptor, and provides the <code class="code">fd()</code> function.
     </p></li></ul></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ext_iterators.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="extensions.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ext_demangling.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 26. Iterators </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 28. Demangling</td></tr></table></div></body></html>